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题库 / Prep2007E1-CR-3
The prairie vole, a small North American grassland rodent, breeds year-round, and a group of voles living together consists primarily of an extended family, often including two or more litters. Voles commonly live in large groups from late autumn through winter; from spring through early autumn, however, most voles live in far smaller groups. The seasonal variation in group size can probably be explained by a seasonal variation in mortality among young voles.
Which of the following, if true, provides the strongest support for the explanation offered?
It is in the spring and early summer that prairie vole communities generally contain the highest proportion of young voles.
Prairie vole populations vary dramatically in size from year to year.
The prairie vole subsists primarily on broad-leaved plants that are abundant only in spring.
Winters in the prairie voles' habitat are often harsh, with temperatures that drop well below freezing.
Snakes, a major predator of young prairie voles, are active only from spring through early autumn.
相关因果（时间关联）。 前提：voles在深秋到冬是以大团队生活，在初春到秋是以小团队生活。结论：团队大小的季节变化是由年轻voles死亡率的季节变化引起的。
问题：什么因素能削弱死亡率导致团队大小的季节变化？否认这个因素能加强结论？
可能的CQ预设：1.（不是）由于非死亡率的第三方因素导致团队大小的季节变化 2.（不是) 团队大小的季节变化导致死亡率的季节变化 3. （不是）由于在特点的地点才有死亡率导致团队大小的季节变化4.（不是）由于死亡率的季节变化导致了A，A导致了团队大小的季节变化。
感觉这样把正取双重否定的想法会把简单的题目复杂化了。
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